Project Abstract With the aging of the American population, the number of older adults at risk for developing cognitive impairment is staggering. Recent research points to age-related change in cognitive performance beginning as early as age 30, highlighting the potential for early interventions. Cognitive function has long been assessed using standardized cognitive tasks administered via neuropsychological evaluation. However, the traditional way to assess cognitive ability is time consuming, requires trained personnel, and requires an office visit. Identifying decline among younger adults is particularly challenging because it can be masked by item redundancy effects. Here we propose developing a new computerized adaptive test (CAT) to assess cognitive function, designed to be administered on computer platforms, that is based on recent advances in multidimensional item response theory (MIRT), with sensitivity to change over relatively short intervals (e.g., two years) among adults over a wide age range. We are calling it CAT-COG. The CAT-COG will assess global cognitive ability as a primary domain as well as 5 cognitive subdomains: episodic memory, semantic memory, working memory, executive function, and processing speed. Our approach will revolutionize computer-based cognitive testing (ultimately in a platform independent way including smartphones), providing precise estimation of an individual?s ability on these domains with minimal respondent burden, using a sufficiently large bank of items so that the same individual?s cognitive ability can be assessed repeatedly without reusing items or stimuli. This project brings together an accomplished interdisciplinary team of researchers and also builds on the unique resources of the Rush Alzheimer?s Disease Center (RADC). These are the key project steps: (1) We will develop a new 1000 item bank of cognitive tasks suited to computational platforms and test them alongside a standard battery of neuropsychological tests through the RADC, including returning cohort participants and newly recruited younger adults. (2) Based on these data, we will develop a computerized adaptive test (CAT-COG) appropriate for measuring global cognitive function and cognitive subdomains across the life course. (3) We will test and validate the CAT-COG among returning RADC participants. (4) We will study short-term variability of the CAT-COG based on daily assessment for a week to determine learning effects and develop a testing protocol that is immune to such effects.